Widget _bottomBar() => AppBar(
        title: Text(PageName.APP_BAR),
        bottom: PreferredSize(
          child: Container(
            alignment: Alignment.center,
            color: RED,
            constraints: BoxConstraints.expand(height: 50),
            child: Text(
              "bottom",
              style: TextStyle(fontSize: 30),
            ),
          ),
          preferredSize: Size(50, 50),
        ),
      );